1.67 rings a bell ------------ You are thinking of the difference in end to end resistance of 2.5/1.5, 1.67 is the multiplication factor, ie, the 1.5 will be 1.67 times greater in resistance than the 2.5.
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every tester ive ever used gives unexpected readings when doing an rcd inco-operated earth loop. this is very common. if the result exceeds acceptable zs simply bridge the rcd and u will get a more accurate result, if its within, dont worry about it
Why would having an RCD in line affect the reading? Is there an appreciable resistance over the contacts? Never had any erroneous readings on my Robin separate when checking Zs with the RCD in line. Maybe these super whizz bang MFT's are not very good?..
This topic has come up before, and it seems fluke and robin testers are the best for giving accurate readings when protected by RCD. Seems odd that test kit manufactors are allowed to use the low current method when its clearly sub-standard to the other method used by robin and fluke. I have changed to a robin loop tester this year for that very reason.
Just whipped out me ol Robin (one of a nest of).. 1..http://farm3.static.flickr.com/2696/4409040455_f05b82bfc2b.jpg 2..Approx 1 min later..http://farm5.static.flickr.com/4031/4409807904_78ee37d469b.jpg Robins are da business peeps..
They are ok, but they won't do loop test's without triping the rcd, unless you use the low current option and then the result's are * I had a Robin KTS1610 at one time, good meter except for the rcd triping problem, also 1610 doesn't have a lead nulling facility, you have to deduct lead resistance from the test reading. [Edited by: admin]